Our initial studies have involved the effect of asbestos and several metal carcinogens, which are often present in trace levels in asbestos, on DNA in human cells. With the alkaline elution technique, DNA-protein crosslinks were detected in fibroblasts exposed to chromate salts. No evidence of repair was seen with up to 12 hours repair incubation after chromate removal from the culture medium. Using an in vitro assay, DNA-protein crosslinks were also detected. In the case of asbestos and nickel, no DNA damage was seen after exposure of fibroblasts to these agents. With the development of methods to maintain human bronchial epithelial cells in culture, DNA damage and repair studies are now being initiated with these cells with particular emphasis on agents implicated in pulmonary carcinogenesis.